Absorbent material and method for making same

ABSTRACT

An absorbent material and method for making same comprising a fiber web, including a fiber blend comprising from about 50 to about 75 weight percent of a fiber having fineness less than about 3 denier and from about 25 to about 50 weight percent of a fiber having fineness ranging from about 3 to about 5 denier wherein the fiber web is bound together by fiber bundles transverse to the plane of the web. The fiber blend may further comprise from about 3 to about 7 percent by weight of a fiber having fineness greater than about 5 denier. The fibers comprising the fiber blend may be entirely hydrophobic, or the about 3 to about 5 denier fiber may be hydrophilic. The absorbent material exhibits a high degree of absorption and fluid retention and does not wet back even under compression. The transverse fiber bundles formed during the mechanical bonding of the web function as wicks for transferring fluid from the surface of the material to the inner portion of the material. The fiber bundles also act as support structures resisting compression and maintaining void space and absorbent surface area within the material, even when wet. The material is reusable and is strong enough to withstand numerous washings. The material is useful as a component of reusable absorbent products further comprising an outer layer or body-side layer. The outer layer may be fluid impermeable, gas permeable or both.

CROSS REFERENCES

"This application is a division of application Ser. No. 08/629,975,filed Apr. 9, 1996 now U.S. Pat. No. 5,677,028.

GOVERNMENT RIGHTS

None

BACKGROUND

This invention generally relates to an absorbent material, and moreparticularly concerns an absorbent material for use in reusableadsorbent articles for the absorption of body fluids as in medical orhygienic absorbents, for example in incontinence products, surgicaldressings and sanitary products.

Absorbent materials are commonly characterized by their capacity toabsorb large quantities of fluid per unit weight of material. A highdegree of fluid retention is also advantageous, so that absorbed fluidis not easily released when the product is subjected to externalpressure, a phenomenon known as "wetting back." Wetting back occurs whenpressure is exerted onto an absorbent material wherein fluids absorbedin the material flow back to and re-wet the surface of the material.Where an absorbent material exhibits a high degree of fluid retentionand no wetting back, the moisture stays trapped within the absorbentmaterial and does not again contact the user.

Generally, absorbent materials exhibiting a high absorbent capacity areavailable as disposable products. Disposable products have heretoforeproven capable of trapping fluids within the material and away from theuser with no "wetting back." The effect is the user stays dry even afterfluid is released.

Reusable absorbent materials commonly comprise textile fabrics due tothe requirement that the materials must be washed and dried betweenuses. Reusable absorbent products have in the past been unremarkable interms of their absorbent capacity. It is true that absorbent materialsincluding hydrophilic fibers tend to absorb a lot of fluid. However,when fluid is absorbed by and wets fabric comprising hydrophilic fibers,there arises a tendency in hydrophilic fibers to lose strength andcollapse causing the fabric to mat down. Void space in the fabric isthereby lost, reducing thickness and limiting the further amount offluid which can be absorbed. Thus, even though the use of hydrophilicfibers enhances absorbency, absorbent materials including hydrophilicfibers tend to have less than optimum absorbency due to wet collapse.

Because of the proclivity of reusable absorbent materials to wetcollapse, reusable absorbent materials tend to wet back, especiallyunder compression. Since absorbed fluid may be forced out of reusableabsorbent material by pressure, reusable absorbent products have beenunable to produce a stay-dry effect with no wetting back.

Further, reusable absorbent products have proven to be uncomfortable.When a material comprising textile fabrics gets wet it stays wetthroughout its entire thickness so that if a user wearing anincontinence garment releases fluid, the wet fabric stays against theuser's skin.

Hence reusable absorbent products have heretofore not been accepted as asatisfactory replacement for disposable absorbent products.

For the foregoing reasons, there is a need for a reusable absorbentmaterial exhibiting a high degree of absorbency for removing fluid fromthe surface of the absorbent material and away from the user's skin. Thematerial must move the liquid rapidly and permanently away from thesurface with no wetting back thereby providing a dry surface against theuser. The reusable absorbent material having this stay-dry effect mustalso be easy to manufacture.

SUMMARY

An absorbent material having features of the present invention whichsatisfies these needs comprises a fiber web including a blend of fibers,the fiber blend comprising from about 50 to about 75 weight percent of afiber having fineness less than about 3 denier and from about 25 toabout 50 weight percent of a fiber having fineness ranging from about 3to about 5 denier, based on a total weight of the blend, wherein thefiber web is bonded together by fiber bundles transverse to the plane ofthe web. The fiber blend comprising the absorbent material may furthercomprise from about 3 to about 7 percent by weight of a fiber havingfineness greater than about 5 denier, based on a total weight of theblend. The fibers comprising the fiber blend may be entirelyhydrophobic, or the about 3 to about 5 denier fiber may be hydrophilic.

The present invention fulfills the needs in the art by also providing amethod for making an absorbent material, the method comprising the stepsof forming a fiber web, the fiber web comprising from about 50 to about75 percent by weight of a fiber having fineness less than about 3 denierand from about 25 to about 50 percent by weight of a fiber havingfineness ranging from about 3 to about 5 denier, based on a total weightof the blend, and mechanically bonding the web providing fiber bundlestransverse to the plane of the web. Alternatively, the fiber web formingstep may comprise forming a web including from about 50 to about 75percent by weight of a fiber having fineness less than about 3 denier,from about 25 to about 50 percent by weight of a fiber having finenessranging from about 3 to about 5 denier, and from about 3 to about 7percent by weight of a fiber having fineness greater than about 5denier, based on a total weight of the blend. The mechanical bondingstep preferably comprises needle punching which may be suitably carriedout in accordance with the present invention at a needle punch densityranging from about 700 to about 900 penetrations per square inch.Further, the method may further comprise the step of cross-lapping theweb to from a layered batt having at least about 8 layers such that theweight of the material is about 8 to about 16 ounces per square yard.

The present invention also overcomes the drawbacks of using reusableabsorbent products through the provision of an absorbent articleincluding an outer layer and an absorbent layer disposed against theouter layer, the absorbent layer comprising a fiber web including ablend of fibers, the fiber blend comprising from about 50 to about 75weight percent of a fiber having fineness less than about 3 denier andfrom about 25 to about 50 weight percent of a fiber having finenessranging from about 3 to about 5 denier, based on a total weight of theblend, wherein the fiber web is bonded together by fiber bundlestransverse to the plane of the web. The outer layer may be fluidimpermeable and gas permeable or slip-resistant. The absorbent articlemay further comprise a body-side layer wherein the absorbent layer isdisposed between the outer layer and the body-side layer. In suchconstruction, the body-side layer and the absorbent layer can be heldtogether by stitch means defining a quilted construction.

Accordingly, it is an object of the present invention to provide a newabsorbent material having one or more of the novel features as set forthabove or hereinafter shown or described.

It is another object of the present invention to provide a method formaking a new absorbent material having one or more of the novel featuresas set forth above or hereinafter shown or described.

Further it is an object of the present invention to provide an absorbentmaterial and a method for making same which material exhibits a highdegree of fluid retention.

A related object of the present invention is to provide an absorbentmaterial and a method for making same which does not wet back even undercompression.

Still further it is an object of the present invention to provide anabsorbent material and a method for making the same which rapidly andpermanently removes fluid away from the surface to the inner portion ofthe material.

Still another object of the present invention is to provide an absorbentmaterial and method for making same which provides the user thereof witha stay dry effect after a release of fluid.

Moreover an object of the present invention is to provide an absorbentmaterial with a high absorbent capacity.

Yet another object of the present invention is to provide an absorbentmaterial and a method for making same for use as a reusable absorbentarticle.

Also an object of the present invention is to provide a simplemanufacturing method for making the new absorbent material of thepresent invention.

A feature of the present invention is the fiber blend used. A highpercentage of a fine denier fiber is employed to provide surface areafor fluid absorbency and retention. Also included in the blend is amedium denier fiber which acts as a carrying fiber for the fine fiberduring processing and provides structural integrity to the finishedmaterial. A small percentage of coarse fiber may be added to the blendto further enhance the structural integrity of the material and provideresistance to wet collapse and wetting back.

Another feature of the present invention is the fiber bundles transverseto the plane of the web formed during the mechanical bonding of the web.The fiber bundles function as wicks for transferring fluid from thesurface of the material to the inner portion of the material. The fiberbundles also act as support structures resisting compression of the bulkfiber matrix thereby maintaining void space and absorbent surface areawithin the material, even when wet.

The absorbent material of the present invention is highly absorbent. Atthe same time, we have observed that the material shows the ability toquickly remove fluid from the surface of the absorbent material andretain the fluid away from the user's skin even under pressure. Thematerial does not wet back resulting in a dry surface against the usershortly after fluid release. The method of making the absorbent materialof the present invention is a simple, efficient productive manufacturingprocess. Moreover, the material may be incorporated into any number ofabsorbent articles, is reusable and is strong enough to withstandnumerous washings.

These and other objects, features and advantages of the presentinvention will become apparent upon reading the following detaileddescription and appended claims.

DESCRIPTION

The present invention is an absorbent material comprising a non-wovenfiber blend. The material comprises one or more intimately blended fiberweb layers formed by carding and cross-lapping. The web is mechanicallybound by needle punching to a predetermined thickness and densitythrough a proper combination of overall fiber weight and needle punchdensity. The interior portion of the needle punched material comprises asubstantial majority of fibers extending generally in the horizontalplane of the material. Needle punching produces a plurality of fiberbundles extending in a direction generally transverse, or vertical, tothe plane of the material for transporting fluid on the surface to theinterior portion of the material. The finished product of the presentinvention is a non-woven absorbent material having a heretofore unseenlevel of absorbency.

The absorbent material in accordance with the present invention may beconstituted wholly by hydrophobic fibers, particularly fibers which areinherently hydrophobic throughout, or a mixture of hydrophobic andhydrophilic fibers. More specifically, the absorbent material comprisesa fiber blend including from about 50% to about 100% hydrophobic fibers,and from about 0% to about 50% of a naturally hydrophilic fiber.

The hydrophobic fibers may be natural hydrophobic fibers or syntheticstaple fibers such as polyethylene, polypropylene, nylon and the like.For use in the present invention, the hydrophobic fiber must be strong,both wet and dry. Preferably, polyester fibers are used as thehydrophobic fiber. A synthetic hydrophobic fiber, such as polyester,owes any inherent hydrophilicity to surface tension. Use of hydrophobicfibers in the material of the present invention results in a veryresilient structure which maintains its loft when wet thereby providingvoid space and surface area within the material for fluid absorbance.

The hydrophobic fibers may be treated with a hydrophilic finish, whichfinish may be applied to the hydrophobic fiber during fiber drawing orfiber blending. A suitable hydrophilic finish for use in the drawingoperation of the present invention is available from Goulstan in Monroe,N.C., U.S.A., under the name NF 2344. For use in the fiber blendingoperation, a hydrophilic finish referred to as Lurol 4126 is alsoavailable from Goulstan. Alternatively, prefinished fibers may bepurchased from a supplier. It is understood that even though thehydrophobic fiber has been coated with a hydrophilic finish, thehydrophobic fiber remains inherently hydrophobic.

The naturally hydrophilic fibers are preferably rayon fibers, orviscose, but may also be any other naturally hydrophilic fibers such ascotton fibers, pulp fibers, and the like, or mixtures thereof.

The fiber web manufactured in accordance with the invention is formedfrom a homogenous blend of the above fibers comprising fine denier fiberand medium denier fiber. Preferably, the fine denier fiber is less thanabout 3 denier and, ideally, the fine denier fiber is as fine aspossible. However, use of fiber having extreme fineness becomesprohibitively expensive. Thus, the lower limit for the fine denier fiberis somewhat limited by practicality and cost.

The fine fibers comprise a major proportion of the blend, ranging fromabout 50% to about 75% by weight of the blend, based on a total weightof the blend, preferably from about 60% to about 70%, and morepreferably about 70% of the blend by weight. The fine denier fiberprovides the basic structure of the fabric and is the primary absorbentfiber in the blend. Having a major proportion of fine denier fiberenhances the number of interstices and surface area within the blend forholding fluid thereby contributing to interfiber absorption. When thefine denier fiber is below about 50% of the blend by weight, theabsorbent capacity of the resulting fabric is reduced. However, aboveabout 75% of the blend by weight the void space within the fabricbecomes significantly reduced diminishing the ability of the fluid tomove through the fabric. Production rate and the cost of manufacturingare also adversely affected. A suitable fiber for use as the fine fiberis sold as Type 54 polyester by DuPont de Nemours, Inc., of Wilmington,Del., U.S.A.

The medium denier fiber has a fineness ranging from about 3 denier toabout 5 denier, and preferably has a fineness of about 3 denier. Themedium denier fiber comprises from about 25% to about 50% by weight ofthe blend, based on a total weight of the blend, preferably from about25% to about 30%, and more preferably about 30% of the blend by weight.In the present invention, the primary function of the medium denierfiber is as a "carrying fiber" to provide structural support to the finedenier fiber during processing. When the medium denier fiber is belowabout 25% of the blend by weight, there is a reduction in productivity.Above about 50%, productivity is improved but fiber surface areaavailable for absorption in the form of the fine denier fibers issacrificed. The medium denier fiber also has some of the attributes ofthe fine denier fibers, providing absorbency to the material, andcontributes to the structural support of the finished absorbentmaterial. A fiber suitable for use as the medium denier fiber is Type794 polyester available from DuPont de Nemours, Inc., of Wilmington,Del., U.S.A.

Alternatively, the medium denier fiber may comprise a naturallyhydrophilic fiber. The fiber blend including naturally hydrophilicmedium denier fibers is primarily intended for use as a component ofbody worn products. As noted above, naturally hydrophilic fiber tends toassimilate released fluid, which is more suitable for a body worncomponent because the absorbed fluid has even less tendency to wet back.A suitable natural hydrophilic material is rayon which is available fromFoss Manufacturing Company, Inc. of Hampton, N.H., U.S.A.

In accordance with the present invention, the fiber blend may furthercomprise a coarse denier fiber having a fineness of at least about 5denier. The coarse denier fiber, although only a small proportion of theblend, adds to the structural integrity of the finished product byproviding compression resistance thereby maintaining the loft of theproduct, especially when wet. This is known as gauge retention or"scaffolding". A fiber having a denier less than about 5 does notprovide sufficient structural support to the resulting material.However, when using thick fibers, the structural benefits of the thickerfiber are outweighed by the loss of handleability of the web.

The coarse denier fiber comprises the smallest proportion of the fiberblend, ranging from about 3% to about 7% by weight of the blend, basedon a total weight of the blend, preferably from about 4% to about 6%,and more preferably about 5% of the blend by weight. When the coarsedenier fiber is above about 7% of the blend by weight, the fabric as awhole loses surface area for absorption. Below about 3% by weight, thebenefits of structural integrity provided by the coarse fiber isreduced. Preferably the coarse fibers are polyester, thereby hydrophobicby nature and unaffected by fluid and possessing good wet strength.Thus, the coarse fibers tend to oppose any wet collapse or compressiveforces for the prevention of wet back, and maintain the gauge of theproduct conserving void spaces within the fabric for absorption. Theparticular fiber used for the coarse fabric is available from FossManufacturing Company, Inc. of Hampton, N.H., U.S.A., under the name ofWhite 550 polyester.

The fibers comprising the fiber blend have lengths suitably ranging fromabout 1.5 inches to about 4 inches, preferably from about 1.5 inches toabout 3 inches, and more preferably about 3 inches. Length is importantfrom a processing standpoint. Above about 4 inches the fiber is too longfor needle punching and tends to pull out or break, shredding the fabricand creating lint and dust. Below about 1.5 inches, the structuralintegrity of the fiber decreases.

The method of making the absorbent material of the present inventioncomprises forming a non-woven fiber web comprising a blend of the abovefibers and subjecting the web to mechanical bonding providing fiberbundles transverse to the plane of the web. Thereafter, the web mayoptionally be subjected to heat treatment by rolling over a heatedcalendar roll to heat shrink and tighten the surface fibers. The latterstep does not enhance the absorbent performance of the product.

The non-woven fiber web may be formed from the fiber blend by well-knownmethods, such as for example, using carding techniques. The web can becross-lapped to provide a web with a plurality of layers having apredetermined combined weight. In the production of the absorbentmaterial of the present invention, the web has between about 8 layersand about 16 layers, preferably between about 12 layers and about 14layers and more preferably about 13 layers. Of course web-making issusceptible to numerous variations. For example, although carded websare described in the present process, it is understood that carded webscan be preformed and supplied as rolls of preformed webs. Non-wovenwebs, other than carded webs which have been formed by air laying,garnetting, and similar processes known in the art, can also beemployed.

The web is mechanically bound, preferably by subjecting the web to aneedling punching operation. As is known in the art, needle punching isa form of mechanical bonding wherein a multiplicity of rapidlyreciprocating barbed needles are driven a controlled distance through abase web thereby reinforcing the web. The barbed needles have a portionclose to the point of the needle which is free from barbs and anotherportion which is provided with barbs. Small bundles of fibers within theweb are caught on the barbs during the forward or reverse movement,respectively, of the needle, or both depending on the type of needleused, and are either pushed forward or drawn backward through the webthereby forming numerous small loci of fiber entanglement. As theneedles move away from the base web the fiber bundles slide clear of theneedle barbs without untangling the transverse interlocked fiber bonds.

The mechanical bonding step of the method according to the presentinvention may be carried out on any type of conventional needle punchloom. The loom may needle punch either from above or from below, or acombination of the two. Preferably, the needle punching operationaccording to the present invention is performed from both sides using anup-punch loom and a down-punch loom. Although any needle punchingconfiguration used for needle punch lines or operations can be used,this preferred process results in only one pass to needle both sides.

The needle punching process results in needles penetrating the surfacesof the fiber web and carrying fiber bundles transversely through theweb. The needle punching may be carried to similar penetration depths oneach side of the web so that a symmetrical absorbent material isobtained, or different penetrations depths may be used. The purpose ofthe needle punching step is to bind the web layers together and providea structure having a reduced gauge with binding fiber bundles extendinginwardly in a direction generally transverse to the plane of the web forholding the layers together.

The particular effects of the needle punching operation, andspecifically the density of the needle punched material, can becontrolled, as is known in the art, by adjusting the needle punchdensity, depth of needle penetration, needle type, fiber type and theproportion of fibers. Generally, the preferred finished density of theabsorbent material of the present invention provides for a very looseconstruction. While needle punching at a higher density, that is, moreneedle penetrations per square inch, will generally strengthen thematerial, a higher needle punching density also produces greatercompaction of the absorbent material resulting in a decrease of overallabsorbent capacity. The resulting structure also becomes more rigidresulting in discomfort to the user. However, there is a point where thematerial will lose its integrity if needled too loosely. Thus, thepreferred density is that density which results in a material which hassufficient structural integrity for its use as a reusable component ofan absorbent product with maximum interior void space and surface areafor absorption wherein maximum absorption capacity is achieved.

For the purposes of the present invention, the needle punch densityutilized is between about 700 and about 900 penetrations per squareinch, preferably between about 750 and about 850 penetrations per squareinch, and more preferably about 840 penetrations per square inch. Aboveabout 900 penetrations per square inch, the material is needle punchedtoo densely reducing the interior void volume and associated absorbency.Conversely, below about 700 penetrations per square inch, the materialis needle punched too loosely and the benefit of increased absorbency isoffset by the lack of internal bond strength needed to hold the materialtogether.

It is understood that a tremendous variety of needles are available andthat the needle punch density effect described above could be achievedany number of ways using different needle types. For example, suitableneedles for the purposes of the present invention include about 38 gaugeto about 40 gauge regular barb felting needles for use in the down-punchloom, and about 38 gauge to about 40 gauge closed barb felting needlesin the up-punch loom.

As discussed above, during the needle punching process fibers in theplane of the web engaged by the needle barbs are carried by the barbsand redistributed to the vertical axis, while those fibers which theneedles do not strike remain substantially in their originalorientation. The inner or middle portion of the material thus has amajority of fibers substantially in the plane of the web. The innerportion also tends to remain very loose so that the material is capableof absorbing and holding fluid. The horizontal orientation of the fibersacts to trap the fluid and positively move fluid on a longitudinal axishorizontally through the material rather than puddling and causing a wetarea.

The fibers which are redistributed vertically by needling extend throughthe material and serve as wicks along which fluid may be carried fromthe outer surface of the absorbent material into the inner portion.These fiber bundles act as capillaries when moisture is present on thesurface. Because the bundles essentially stand vertically through thepad, they carry the liquid down into the horizontally oriented fibers.The wicks thus function to enhance fluid transfer between the surfaceand the interior of the material. Fibers laying in the horizontal planeof the fabric rapidly transfer the fluid longitudinally throughout thepad thereby spreading the fluid throughout the material. Thus, the fluidis taken from the top surface by the vertical fiber bundles and into thecore of the material where it then moves out laterally. In effect,vertical fluid pathways access horizontal fluid pathways to provideabsorbency to the material. Because the vertical fiber bundles act aswicks to guide the fluid from the outside layer to the inner portion ofthe material, the outside layer effectively remains dry even after fluidis released by the user.

While the preferred method for mechanically bonding the fiber web inpreparing the absorbent material of the present invention is needlepunching, it is understood that needle punching is not the only means bywhich fibers from within the fibrous layer can be caused to form thewicks in accordance with the invention. For example, wicks can be formedby means for quilting, stitch bonding, air jets or hydroentanglement,using very high pressure water jets directed at one or both free facesof superimposed fibrous webs. In any case, the purpose is to bond theweb forming vertical fiber bundles to transfer liquid to the interiorportion of the material where the liquid is transported from the pointof discharge throughout the material. The vertical fiber bundles alsoprovide structural support to the finished material to keep the materialfrom collapsing, even when wet. This compression resistance maintainsthe void space and fiber surface area within the pad which results inmore volume available for fluid absorbance. Through the combined effectof the vertical bundles providing structural integrity and fluidtransfer into the interior of the fabric and the horizontal fiber layersspreading fluid throughout the inside of the fabric, wet back isprevented even under pressure because the fluid remains trapped withinthe material. As noted above, use of hydrophobic fibers in the fiberblend, and particularly the coarse fibers, also adds to the compressionresistance and helps maintain the structure of the material during use,especially when the material becomes wet.

The absorbent material of the present invention has a finished weight ofabout 10 to about 15 ounces per square yard, preferably about 12 toabout 14 ounces per square yard, and more preferably about 13 ounces persquare yard.

The thickness of the finished product largely depends on the loomconfiguration and needle length. Although, if needle punched too thinly,the material is less absorbent and the ability to provide structuralintegrity to the material through needle punching is lessened. If needlepunched too thickly, the needle punching becomes less efficient and thematerial loses the benefits of the vertical bundles for moving the fluidto the interior region. The thickness of the absorbent material of thepresent invention can range from about 0.130 inches to about 0.230inches, and is preferably about 0.18 inches.

Optionally, the needle punched web may also be subjected to a heatedcylinder roll, which is suitably carried out by passing the web slowlyover a heated calendar roll to press and smooth one surface. The hotroll tends to provide a smooth lint free surface which is important insome applications. The fiber thereafter has a noticeable difference intightness, and good drape and handle. Without heat, the fabric is proneto have a more loose surface. The heat treatment also helps in theshrinkage of the fibers for improved overall durability of the fabricand protects against post-use shrinkage. Heat setting or preshrinking ofthe material adds to its longevity because it prevents any chance of thefabric deforming in laundering or drycleaning operations which allowsmarketing of a product by size without fear of shrinking during use andreuse. Exposure to the heated calendar roll, however, does not enhancethe absorbent performance of the material.

The absorption capacity of a material is typically measured as apercentage of its original weight after the fabric is saturated with aphysiological saline solution. Excess liquid is allowed to run off for agiven period, and then the finished piece is weighed and the differencebetween the weight of the finished piece and the weight of the saturatedpiece as a percentage of its original weight is calculated as a measureof absorbency. It is unusual to find a non-woven absorbent producthaving an absorption capacity consistently above 800%. We have observedthat the material of the present invention has an absorption capacity ofat least 800%, and has achieved absorption capacities of about 1300%.For example, a 36-inch square piece of material weighing 13 ounces persquare yard can absorb about one hundred thirty ounces (130 oz.) byweight of fluid. In other words, the 36-square inch piece of materialincorporated into a garment or bed pad can absorb about one gallon, morefluid than most users can discharge in a day.

The absorbent material of the present invention may be used in anynumber of absorbent articles and products, either alone or as acomposite. In one aspect, the reusable absorbent material of the presentinvention may be incorporated into a final product for use in medical orhygienic adsorbents for the absorption of body fluids, for example inincontinence products especially undergarments and briefs, baby diapers,absorbent pads, surgical dressings and sanitary products.

At a minimum, absorbent articles comprise a layer of absorbent material.The articles may also be provided with a moisture impervious outer layerto protect clothing or whatever object in the physical surroundingswhich the article may contact. The outer layer is typically a plasticsheet, such as polyethylene or propylene, which is normally stitched oradhesively attached to the material. Alternatively, an impermeable outerlayer may be applied as a hot liquid as a final step in the method ofmaking the absorbent material of the present invention. In thisapplication step, hot liquid urethane or vinyl is coated on a surface ofthe material following the needle punching or can rolling step. Theurethane or vinyl is allowed to cool forming an impermeable surface onthe absorbent material. The material of the present invention thusdemonstrates the unique structural strength and heat resistance toaccommodate this process without burning, melting or shrinking.

Preferably, the outer layer material, in addition to being fluidimpermeable, is also gas permeable. In this configuration, the absorbentarticle is rendered "breathable." The term "breathable" as used hereinmeans that the gas permeable outer layer allows passive airflow throughthe article permitting air to freely associate with the layers of thearticle. Any suitable material exhibiting fluid impermeable, gaspermeable properties may be used. Preferably the material is lightweightto facilitate the handling of the absorbent article. An example of amaterial usable as the outer layer is GORETEX® which is manufactured byand available from W. L. Gore Company of Elkton, Md., USA. Thebreathable outer layer, by allowing passive airflow through theabsorbent article, facilitates drying of the material and reduces heatbuild-up near the user's skin thereby reducing or eliminating conditionswhich lead to or aggravate skin irritation, bed sores and the like.Because the absorbent article can dry quickly without removing the usertherefrom, the absorbent capacity of the article is not limited by theamount of retained moisture. As a result of this advantage, the articleincorporating the material of the present invention has to be changedand washed less often than previous absorbent products and is thereforeless expensive to use.

Absorbent pads may also be provided with a slip-resistant outer layer toprevent the pads from slipping out of position when a user moves aboutwhile sitting, lying or standing on the pad, which ensures protection ofthe underlying article from, for example, the incontinent user'sexcrements or fluids. To accomplish slip-resistance, the underside ofthe moisture impermeable layer can be treated with a slip-resistantcoating while retaining the moisture impermeable characteristics of thebottom layer and at the same time preventing slippage of the pad. Anysuitable slip-resistant coating can be used as is well known in the art.Preferably, the slip-resistant coating is polyvinyl chloride which isavailable from Bradford Industries of Lowell, Mass., U.S.A.

Optionally a layer of soft, non-reflective, non-abrasive material may bepositioned over the absorbent material and next to the clothing or skinof a user. The body-side layer is preferably in the form of a fabriclayer and more preferably is a knitted polyester fabric. The knittedpolyester fabric may be obtained from any suitable source such asGuilford Industries of Greensboro, N.C., U.S.A. However, it is to beunderstood that the body-side layer may be made of other materials andother knitted, woven or non-woven constructions as desired and as arewell known in the art. Preferably the body-side layer is permeable tobut does not absorb moisture, and does not shift, flatten, or lump afterwashing. The body-side layer of the absorbent article positions itselfnext to the user's skin to prevent chafing, aid in the prevention andaggravation of bed sores and can be used as padding. The body-side layerfabric also absorbs and conducts radiated body heat to the absorbentmaterial which acts to vent such heat through the breathable outer layerthereby reducing heat in the area of the skin tissue of the user. Theabsorbent material and body-side layer may be held together by stitchmeans through the two materials pulling the layers together in aplurality of locations and defining a quilted construction.

Instead of an added body-side layer, the method of making the absorbentmaterial of the present invention may incorporate an embossing stepwherein a surface of the material is embossed using a heated rollingdie. Due to the unique structural properties of the present material,the resulting absorbent material withstands the embossing step withoutadverse effect to its absorbent properties. The embossed materialpresents a tight, yet soft body-side layer.

The body-side layer of the absorbent article may have a hydrophilicfinish and/or an antimicrobial finish. The hydrophilic finish assuresrapid dissipation and absorption of fluid into the absorbent materialleaving the entire top surface of the pad coming into contact with theskin or clothing of the user feeling substantially dry. Theantimicrobial finish assures that any bacteria coming into contact withthe finish will be killed upon continued contact with the finish. Anysuitable hydrophilic or antimicrobial finish known in the art may beused. An exemplary hydrophilic finish which has been used is Milatesewhich is available from Guilford Industries of Greensboro, N.C., USA.

Where the absorbent article is for use as a wound dressing, a suitablenon-stick, gauze-like material may be used as the body-side layer. Onesuch material is DELNET, which is available from Foss ManufacturingCompany, Inc. of Hampton, N.H., U.S.A.

The layers may be secured together by any suitable means known in theart including binding tape, whip-stitching, adhesives, lamination andthe like. For example, for absorbent pads the preferred securing meansis binding tape which overlaps the layers of the pad and is bound to theedges of the pad by means of stitching. Stitching surrounds the outerperimeter of the absorbent pad and is stitched to the top and bottom ofthe binding and through the respective layers. The binding tapesurrounds and protects the peripheral edges of the layers and definesthe peripheral outline thereof. The binding tape may be any suitabletape known in the art and may be made of any suitable material.Preferably the binding tape is made of polyester.

The article comprising the absorbent material of the present inventionis suggested for use as a reusable, washable undergarment or brief orabsorbent pad for nursing homes, hospitals and state and federalinstitutions. For example, an undergarment or pad has particular use inkeeping an incontinent patient, a surgical patient or anyone subject tothe drainage of body fluids dry and comfortable while also protectingclothing, bedding and other furniture from damage. For this use, theundergarment is worn or the pad is placed on top of the patient'sbedding or wheelchair with the outer layer facing against the bedding orchair. Thus, the absorbent material serves to absorb the patient'sexcrements of fluid while the fluid impervious outer layer preventsthese excrements or fluids from passing through and wetting or soilingclothing, the bedding material or the chair fabric upon which the pad isplaced. The absorbent article of the present invention can also be usedas a mattress pad for a burn bed, a bumper pad, a baby's crib pad, as adiaper or an apron or vest with the same idea incorporated, that theclothing will be protected from liquid. The absorbent pad is easilyadaptable for use on a bed, chair, wheelchair, or the like. Absorbentunderpads placed on tables such as operating tables, examination tablesand the like serve a similar function. Absorbent pads may also be usedas sanitary pads adjacent to toilets or urinals and, if flame-resistant,as a safety pad adjacent to stoves or the like where grease and otherliquids may be spilled.

The previously described embodiments of the present invention have manyadvantages, including an aversion to wetting back due to the material'scompression resistant properties preventing wet collapse. The fiberstructure of the material combined with the high interior void space andsurface area results in an absorbent material which effectively andrapidly acquires and holds fluid thereby preventing the fluid fromreturning to the surface of the material even under pressure. Thus, theliquid stored in the interior of the absorbent is no longer able topenetrate the surface layer to re-wet the exterior.

Further, the open, loose nature of the fabric enhances the absorptioncapabilities of the present invention. Fluids do not have to penetrate adense fiber composition, thus eliminating a source of pooling and theneed for pressure or effort to push the fluids through the fabric. Theabsorbency and retentivity of the material of the present invention areof a level normally associated with more highly absorbent materials,including hydrophilic materials such as rayon and cotton which aresubject to wet collapse.

Another advantage of the present invention is the material's ability toquickly and permanently remove wetness from its surface. Due to theincreased surface area for absorbance within the fabric and the actionof the vertical bundles wicking fluid into the interior away from thesurfaces and trapping the fluid within the interior of the fabric, thesurface of the material feels dry even when a considerable amount offluid is within the material. Also, once the surface is wetted, thepower of the material to draw the fluid into the inner portion providesa dry surface layer. An incontinent undergarment or brief or absorbentpad conforming to the present invention displays the advantage that itcan absorb a large quantity of fluid which does not again reach thesurface of the absorbent material with the result that the surface ofthe material becomes dry again. This "stay dry" effect has heretoforenot been available in a reusable absorbent material. Thus, the presentinvention represents the first reusable absorbent material with a staydry effect with no wet back in combination with dramatic absorbency.

As used in a breathable absorbent article, such as for use by anyonesubject to drainage of body fluids, the absorbent material providesmaximum absorbency and comfort to persons coming into contact therewithand further results in a dried fluid absorbent layer a very short timeafter such layer becomes wet. The material is comfortable and does notcollapse when wet continuing to provide cushioned protection.

Moreover, the material of the present invention is a durable heavy dutyfabric intended primarily for use in reusable and washableundergarments, briefs, pads and other hygiene products. The material isdesigned to withstand countless machine washings and shows the abilityto withstand exposure to soap, bleach, and high temperatures of wash anddry cycles using regular institutional laundry procedures withoutsignificant loss in its absorbency or other properties. Because it ismanufactured of light-weight materials, it dries rapidly.

The material is available in roll form for easy conversion to pads orother uses. The material is easily cut and trimmed without fraying andproduces components with good dimensional stability. Absorbent articlesconstructed in accordance with the teachings of the present inventionmay be dispensed individually wrapped and in sterile condition in paperenvelopes or in unsterile rolls of the material so that attendants maycut from the rolls pads of desired size. Depending on its use, anabsorbent article can be manufactured of any size, such as for thecomplete protection of a standard hospital bed or for use in a chair orwheelchair. The layers can be dye cut to desired dimensions and theedges can be sealed by binding tape and stitching. Where the articlecomprises more than two layers it is preferably quilted to prevent themoisture absorbent layer from bunching up or shifting.

Construction of the reusable absorbent material may be shown by thefollowing nonlimiting example. A homogenous fiber blend was producedcomprising 70% by weight of 1.5 denier, 1.5 inch fibers; 25% by weightof 3 denier, 3 inch fibers; and 5% by weight 7 denier, 3 inch fibers.Prior to being needle punched, the fibers were run through highefficiency cards to produce an open web of about 0.5 to about 1.0 ouncesper square yard. The web was then cross-lapped to give a batt with 13layers. Needle punching was performed using a Fehrer NL/9S tacking loomas the down-punch loom, and a Fehrer NL/21R/S as the up-punch loom. Highefficiency 38 gauge tacking needles were used in both needle loompositions. The looms had a needle punch depth of about 0.35 inches and aneedle punch density of 840 penetrations per square inch. The finishedfabric had a weight of about 13 ounces per square yard and a gauge ofabout 0.180 inches. As a finishing step, the material was rolled over anoil-heated can at a temperature of about 370° F. The time spent on thecan was about 36 seconds. After rolling over the can the fabric wascooled at ambient temperature. The resultant fabric had an absorbency ofabout 1000%.

While the present invention has been described in considerable detail inconnection with particular embodiments thereof, it will be understood,of course, that we do not intend to limit the invention to thoseembodiments since modifications may be made by those skilled in the art,particularly in light of the foregoing teachings. For example, thedisclosed absorbent material may have a myriad of uses outside thepersonal hygiene and incontinence areas. On the contrary, we intend tocover all alternatives, modifications and equivalents as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims. It is, therefore, contemplated by the appended claims to coverany such modifications as incorporate those features which constitutethe essential features of these improvements within the true spirit andthe scope of the invention. Therefore the spirit and scope of theappended claims should not be limited to the description of thepreferred versions contained herein.

I claim:
 1. A method for making an absorbent material, the methodcomprising the steps of:forming a fiber web, the fiber web comprisingfrom about 50 to about 75 percent by weight of a fiber having finenessless than about 3 denier, from about 25 to about 50 percent by weight ofa fiber having fineness ranging from about 3 to about 5 denier, and fromabout 3 to about 7 percent by weight of a fiber having fineness greaterthan about 5 denier, based on a total weight of the blend, andmechanically bonding the web providing fiber bundles transverse to theplane of the web.
 2. A method for making an absorbent material asrecited in claim 1, wherein the web forming step comprises providing acarded non-woven fiber web.
 3. A method for making an absorbent materialas recited in claim 1, further comprising the step of rolling thematerial over a hot can.
 4. A method for making an absorbent material asrecited in claim 1, wherein the mechanical bonding step comprises needlepunching.
 5. A method for making an absorbent material as recited inclaim 4, wherein the needle punching step comprises using a needle punchdensity ranging from about 700 to about 900 penetrations per squareinch.
 6. A method for making an absorbent material as recited in claim1, further comprising the step of cross-lapping the web to from alayered batt.
 7. A method for making an absorbent material as recited inclaim 6, wherein the cross-lapping step comprises forming a batt havingat least about 8 layers.
 8. A method for making an absorbent material asrecited in claim 1, further comprising the step of applying a fluidimpermeable coating to a surface of the web.
 9. A method for making anabsorbent material as recited in claim 1, further comprising the step ofembossing a surface of the web.